Almost two billion people live without a reliable source of electricity, but they may not have to live without refrigeration. In a simple, rugged twist on the gas-fired refrigerator, a prototype gadget uses heat from fire to create a cheap source of cooling. The cylindrical device, 10 centimeters in diameter and 20 centimeters long, has a chamber on each end-one made of steel and the other of aluminum. The chambers are separated by a ceramic insulator fitted with two valves. To charge the unit, a user places its steel side on a fire for 30 minutes. A liquid coolant in the steel chamber turns into gas and passes through a oneway valve into the aluminum chamber.
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